NJHD stands for New Jerusalem and Its Heavenly Doctrine and is a short summary work written by Swedenborg after his 8 volume (in Latin) Arcana Coelestia. At the end of each chapter (which are on topics such as the internal and external man, conscience, and temptation) there are extensive references to places in Arcana Coelestia where that topic is discussed more fully. Having all of those references hyperlinked makes it much easier to look them all up.